The invention relates to new oxazolidinones of the formula I ##STR2##
Z is O or S,
R.sup.1 and R.sup.2 are each phenyl or benzyl radicals which are unsubstituted or mono- or disubstituted by alkyl, alkoxy, alkylthio, alkylsulfinyl and/or alkylsulfonyl having each 1-4 C atoms, alkanoyloxy and/or alkanoylamino having each 1-6 C atoms,
F, Cl, Br, OH and/or CF.sub.3 or are heteroaryl radicals containing 1-4 heteroatoms and
R.sup.3 and R.sup.4 are each H, alkyl or alkoxy having each 1-4 C atoms or are F, Cl, Br, OH or CF.sub.3, and also salts thereof.